1. Field of the Invention
The present invention relates to a substrate used for processing a wafer.
2. Discussion of Related Art
A preparation method for a semiconductor device that includes a back-grinding process or dicing process, during which a sheet such as a surface protective sheet or dicing sheet is used.
Recently, since the demand for compact and lightweight semiconductor devices has increased, the performance of such a sheet for processing a wafer has accordingly become more and more important.
For example, in order to make a circuit having a higher degree of integration than a conventional method in which a circuit is formed only on one side of a wafer, circuits should be formed on both sides of a wafer. In order to form circuits on both sides of the wafer, the wafer to which a processing sheet is attached should be subjected to a high-temperature process. Thus, the sheet for processing a wafer requires excellent heat-resistance or dimensional stability at high temperature. However, when a hard substrate having a high melting point is used in order to secure heat resistance and dimensional stability, protection of the wafer is degraded and stress relaxation is also reduced, leading to a higher probability of damage to the wafer.
The sheet for processing a wafer should have excellent stress relaxation properties and have no protrusions such as fish eyes. When the stress relaxation properties are reduced or a protrusion is present on the sheet, the wafer becomes easily damaged due to residual stress or due to non-uniform pressure. Such a phenomenon is more common due to the demand for a wafer having a large diameter and small thickness.
Regarding the sheet for processing a wafer, excellent cuttability is required. When cuttability is decreased, a cutting defect may occur during the process, and thus wafer processing may be discontinuously performed. Consequently, when the cuttability of the sheet for processing a wafer is decreased, production efficiency can be reduced and the wafer can be damaged.
Korean Patent Publication No. 2006-0047526 discloses an adhesive sheet having a specific range of storage modulus for the prevention of damage to a wafer, even when being applied to a thin film of the wafer.
However, there are no currently-known techniques, including Korean Patent Publication No. 2006-0047526, for a sheet for processing a wafer that satisfies all of the properties as described above.